Gravel-packing method



' Nov. 9, 1965 G. c. HOWARD ETAL 3,216,497

GRAVELFPACKING METHOD Filed Deo. 20, 1962 2 Sheets-Sheet 1 CLARENCE R.FAST GEORGE C. HOWARD INVENTORS ATTORNEY N0V- 9, 1955 G. c. HOWARD ETAL3,215,497

GRAVEL-PACKING METHOD 2. Sheets-Sheet 2 Filed Dec. 20, 1962 FIG. 5

FIG. 4

CLARENCE R. EAST GEORGE c. How/.mn mvENToRs Qwjfe/ ATTORNEY UnitedStates Patent O 3,216,497 GRAVEL-PACKING METHGD George C. Howard andClarence R. Fast, Tulsa, kla., assignors to Pan American PetroleumCorporation, Tulsa, kla., a corporation of Delaware Filed Dec. 20, 1962,Ser. No. 246,627 4 Claims. (Cl. 166-19) This invention concerns a methodof preventing the flow of sand particles into a well as fluids enter thewell from an unconsolidated sand formation. More particularly, themethod comprises placing a gravel pack in a washed-out sectionsurrounding a well casing by first sealing existing perforations in thecasing, then perforating the casing at the upper and lower extremitiesof the washed-out section, and thereafter circulating a slurry of gravelbetween the new perforations until the section has been completelypacked with gravel.

A well producing from an unconsolidated formation is usually completedby first cementing a casing through the formation, and then perforatingthe casing and cement sheath at intervals throughout the producing zone.If the well is then placed on production without further treatment orsafeguards, sand usually is carried into the well along with theformation fluids. Aside from the abrasive effects of the sand on thecasing, tubing, and flowing or pumping equipment, a washed-out sectionor cavity develops outside the casing. This sometimes results incollapsed casing when caving occurs in the cavity.

Over the years, many techniques have been tried for placing a gravelpack in a well to separate and exclude sand fines from the producedfluids. In general, these packs have been put in place either by pumpinga gravel slurry through all of the perforations simultaneously, with thecarrier liquid filtering into the formation; or the gravel has beenfirst deposited in the bottom of the well, and a screen is then loweredon a tubing and washed down into the gravel by circulating liquid toiluidize the gravel. In some instances, -the sand has been excludedsatisfactorily. In others, success has been short-lived. Sand productionresumed after only a brief period of exclusion.

An analysis of these successes and failures usually does not reveal thatany particular type of gravel or screen for retaining the gravel issuperior. Instead, the degree of success frequently appears to correlatewith the extent to which the washed-out or open section of theunconsolidated formation has been filled with gravel. It is now believedthat an incomplete fill-up of gravel between the unconsolidatedformation and the screen enables the gravel particles to move about asfluids flow from the formation into the well. The result is that thesmall sand particles also can move through the loose gravel to thescreen. The openings in the screen usually are large enough to passthese sand fines but not the gravel. As these sand particles enter thewell, the section not filled with gravel enlarges. Continual movement ofthe gravel and sand abrades the screen until holes large enough to passthe gravel also may be worn in it, whereupon the well must be shut inand repaired.

We have now developed a method of gravel-packing a washed-out sectionoutside of a perforated casing which produces a substantially completefill-up of gravel, thereby preventing movement of the gravel particlesas iluids flow through. Thus, instead of allowing passage of saidgrains, they are effectively filtered from the flowing iluids so thatfurther washing-out cannot occur.

It is therefore an object of our invention to produce an effective andimproved gravel pack in a washed-out section of unconsolidated formationoutside of a perforated casing. Another object is to confine anunconsolidated 3,216,497 Patented Nov. 9, 1965 sand formation andsubstantially completely prevent movement of the sand particles asfluids flow from the formation into the well casing. A further object isto prevent the entrainment of solid particles in the fluids entering thewell. A still further object is to prevent abrasion and erosion of thewell equipment by sand particles entrained in the fluids entering a wellfrom a producing formation.

These objects are accomplished by the novel method which we havedeveloped for placing a gravel pack in a well, which method comprisesfirst sealing off all existing perforations, then carefully positioningnew perforations with respect to the cavity to be filled, circulating acarrier liquid and gravel particles through these perforations to fillthe cavity completely, and then resuming production through the gravelpack in such a way as not t0 disturb the pack particles. This methodwill now be described in more detail by referring to the accompanyingdrawings. In these drawings:

FIGURE 1 illustrates in cross-section a typical well having a washed-outsection in the formation adjacent a perforated well casing;

FIGURE 2 shows the well with the original casing perforations sealed andnew perforations made near the upper and lower extremities of thewashed-out section;

FIGURE 3 shows a gravel-retaining screen and gravelplacement equipmentin position to fill the washed-out section;

FIGURE 4 illustrates the removal of excess gravel from the well afterthe cavity behind the casing has been lled with gravel; and

FIGURE 5 shows the completed gravel pack with the production tubingre-installed to withdraw well fluids.

Referring to FIGURE l, an oil-producing formation 11 is penetrated by awell 9 having casing 10 therein. Fluids from the formation enter thecasing through perforations 13 and are withdrawn from the well throughtubing 14, suspended in well head 15. Gas may be drawn lfrom the wellannulus via flow line 16 at the well head. A washed-out section orcavity 12 `surrounding the perforated section of the casing 10 isrepresentative of the cavities which are produced by the flow ofsand-containing fluids into the well, when formation 11 is a poorlyconsolidated sand.

In FIGURE 2 the well 9 is shown with the original perforations sealedand new perforations 17 and 1 respectively near the lower and upperextremities of cavity 12. An impermeable liner 25 covers the originalperforations, which may also be filled with plastic plugs 30.

An apparatus which may be employed to circulate gravel into the cavity12 is shown in FIGURE 3. The apparatus is attached to a tubing 24 at athreaded connection 23 in a valve body 22. A ball check 19 is heldagainst the seat 21 of valve 22 by a spring 2t) to prevent back-flow ofgravel into the tubing. A slotted or perforated screen 26 extends abovethe check valve assembly 22 to a point just above upper perforations 18to prevent the ilow of gravel into the well. An annular seal 27 abovethe upper perforations 18 and between liner 25 and screen 26 preventsilow of gravel and carrier liquid upwardly past the top end of screen26. A lower annulus seal 28 on valve body 22 is provided to prevent flowof gravel slurry either upwardly from the check valve outlet, ordownwardly past the valve outlet from upper perforations 18. The gravelslurry passing down through check valve 22 is thus forced to flowoutwardly through perforations 17 during pack placement.

Preferably, but not necessarily, the outer surface of screen 26 iscovered by a sleeve 29 over most of its length, from seal 27 downwardlyto a point near but somewhat above the lower end of the screen. By thusleaving open 3, the slots in screen 26 immediately above valve body 22,a downward circulation of gravel slurry to completely pack the annularspace between seals 27 and 28 and between liner 25 and screen 27 isassured. If sleeve 29 is omitted, however, gravel particles will usuallysettle out by gravity and lill this space, as the carrier liquid flowsinwardly through the screen openings.

FIGURE 4 illustrates the removal of excess gravel from the wellfollowing placement of gravel 31 in the cavity 12 outside the casing 10.Tubing 24 is disconnected from valve body 22 at back-olf threads 23 andraised a short distance so that a flushing liquid can be circulated downthe tubing and up the inside of screen 26 and casing 10 to discharge theexcess gravel through flow line 16 at the well head. Also, a solvent forthe material of sleeve 29 forming a temporary seal may be depositedinside the screen 26 after the excess gravel has been circulated out.

The completed gravel pack is shown in FIGURE 5 with production tubing 14re-installed. Gravel 31 completely lls the cavity 12 which had beenwashed out in the unconsolidated formation 11. Spring 20 holds ballcheck 19 against valve seat 21 so that uids cannot enter the well atlower perforations 17 and carry gravel into the screen and tubing.Fluids entering the well through upper perforations 1S are iilteredthrough the gravel and screen between annular seals 27 and 28.

In carrying out our invention, production tubing 14 is rst removed fromthe well 9. Thereafter, perforations 13 in the well casing are plugged.We prefer to plug these perforations by one of the methods which havebeen developed recently for repairing leaks in casing. U.S. Patents3,028,915 (Jennings) and 3,047,065 (Vincent) teach methods for placing aglass ber and resin liner inside a well casing so that the perforations13 are lled by plugs 30 of synthetic resin or plastic material.

In the alternative, the perforations 13 may be sealed with a steel liner25 as shown in FIGURE 2.

This method for sealing holes in casing utilizes a steel liner havinglongitudinal corrugations so that it is of reduced diameter and can becoated with an adhesive such as epoxy resin, then lowered into thecasing and expanded by smoothing out the corrugations, producing astrong, cylindrical liner, tting snugly inside the casing. A portion ofthe resin is extruded into the perforations, forming the plugs 30therein. A detailed description of this method for placing the steelliner inside a well casing is given in the paper by Vincent et al. inthe Society of Petroleum Engineers of AIME, Production ResearchSymposium, Tulsa, Oklahoma, Apr. l2-l3, 1962, pages 21-28.

After liner 25 has been installed and perforations 13 plugged,perforations 17 and 18 are made near the lower and upper extremities ofthe washed-out section. lt is desirable that the perforations in eachset be at substantially the same level. Shaped-charge casing perforatorsare presently available which can make as many as eight perforations ina single horizontal plane at one ring. One of these charges is fired ateach level to produce the necessary perforations. As all of theformation fluids will enter the casing 10 through perforations 18 insubsequent producing operations, the perforations should have as large atotal area as possible, so that the fluids pass through at low velocity.This helps avoid erosion of the screen 26.

With the liner 25 installed and perforations 17 and 18 made at oppositeends of the cavity 12, apparatus is assembled to place gravel in thecavity. The threaded connection 23 for attaching check valve body 22 totubing 24 is preferably one that can be disconnected easily, such as isused in tubing safety joints. These joints typically have either rightorleft-handed coarse threads which can be unscrewed at low torque wheneither tension or compression is applied to the tubing joint. Screen 26is attached to the top of valve body 22 by welding or in any othersuitable way. The screen may be woven wire,

wound wire, or a slotted tubular sleeve of any suitable type ordinarilyused to support a gravel pack. Rubber swab cups or similar devices areattached to the outside of the screen and valve body to form the annularseals 27 and 28. Temporary sealing sleeve 29 is then applied to thescreen from seal 27 downwardly to within a few inches of the bottomscreen openings. This sleeve is desirably produced by coating the screenwith a material which can be dissolved in oil, water, or other solvent.ln situations where there is no oil standing in the well and the gravelcan be placed in an aqueous slurry, paraffin Wax or an oil-solublehydrocarbon resin such as that taught in U.S. 2,067,073, Carmody, may beused to coat the screen. In situations where the screen will becontacted with oil, the coating should be a water-soluble material suchas sugar, starch, polyvinyl alcohol, sodium chloride, or other similarcompound which can be crystallized on the screen, then subsequentlydissolved with water. Where both oil and water may be encountered duringplacement of the gravel pack, the screen can be covered with a thinsheet of metal such as magnesium, which is dissolved later withhydrochloric acid. Another suitable type of sealing sleeve 29 is thatproduced with a polymer such as polyvinyl chloride or polyvinyl acrylatewhich can be later dissolved with tetrachloroethylene.

This screen assembly is then lowered into the well on tubing 24 untilupper annular seal 27 engages the upper end of liner 25. The Seal shouldenter the end of the liner, but care should be exercised to avoidlowering it as far as upper perforations 18. Although the length ofscreen 26 and the position of lower seal 2S and check valve body 22relative to lower perforations 17 are not critical, it is generallypreferred to place the check valve 22 only a short distance above thelower perforations. In this position the screen is opposite the upperperforations, with upper and lower seals 27 and 28 respectivelydirecting flow from the upper perforations 18 through the screenopenings.

With the screen assembly positioned as described above, a slurry ofgravel in a carrier liquid is pumped down the tubing, through the checkvalve 22 and into the casing adjacent the lower perforations 17. Theslurry passes through these perforations into cavity 12 surrounding thecasing. After the slurry fills cavity 12, it then enters perforations1S, and gravel filters out against the screen 26 between annular seals27 and 28 as the carrier uid flows through the unsealed section of thescreen above the lower seal. After the annulus between the screen andliner segregated by these seals has been filled with gravel, furthercirculation of the slurry packs the gravel in the cavity with thecarrier-liquid ltrate either passing out into formation 11 or beingremoved through perforations 18 and the screen 26, and then up thecasing annulus. With circulation in this manner, the gravel has atendency to pack the cavity from the top to the bottom, therebyproducing a uniform pack. The upward flow of the slurry agitates orfluidizes gravel particles which otherwise might settle toward thebottom of the cavity and produce a bridge before the cavity iscompletely lled with gravel. When the cavity 12 becomes packed withgravel, continued circulation of the slurry iirst packs the casing 10below the check valve 22 and then gravel begins to back up in the tubing24. When a pronounced and continuing increase in injection pressuresignals this condition, slurry circulation is discontinued.

After the pack has thus been placed, it is necessary to withdraw slurrycirculation tubing 24 without permitting movement of the gravel pack.This is accomplished simply by disconnecting the tubing at back-olfconnection 23 so that the check valve 22 retains the gravel. Aftertubing 24 has been disconnected, it is lifted about one foot above thevalve body and gravel-free liquid is circulated down through the tubingand up through the screen and casing annulus to remove the excessgravel, as shown in FIGURE 4. As an alternative to direct circulationdown the tubing, up the annulus and out flow line 16, reversecirculation down the annulus and up the tubing may be used to remove theeXcess gravel.

Following the gravel clean-out step, a solvent for temporary seal sleeve29 is circulated down the tubing and discharged inside the screen abovethe check valve. The solution of the sealing material in the solvent maybe removed either by circulating it from the well or by displacing itinto the formation. It is to be understood that the thickness of sleeve29 is small enough that dissolving it does not cause or allow anyappreciable movement of the annulus pack particles.

The gravel-placement tubing 24 is then withdrawn and replaced byproduction tubing 14 as shown in FIGURE 5. Although fluids from theformation can enter the well only through the upper perforations 18, theentire area of the screen 26 is open to let the iluids flow into tubing14. The gravel used in forming the gravel pack according to oneinvention may be any of a number of different hard, inert materialsincluding nutshells, sand, gravel, limestone, glass, and the like. Forthe most effective sand restraining ability, the particle size of thegravel should be selected on the basis of the particle size of the sandto be restrained. Gravel, 85 weight percent of which passes a 40-meshand is retained on a 60-mesh screen, U.S. Standard sieve, is suitablefor many of the unconsolidated sand formations in the United States GulfCoast area. Also, it has been found that the particles in the pack areless likely to move and allow sand passage if they are angular in shaperather than rounded. Thus, we prefer to use gravel produced by crushinglarger particles, and then screening to recover the desired particlesizes. The carrier uid may be water, crude oil, or a petroleum fractionsuch as fuel oil.

Although we have described our invention as a procedure wherein thegravel slurry is injected at the lower end of the washed-out zone, itshould be understood that the zone could be packed by injecting theslurry at the upper perforations and withdrawing the ltrate at the lowerperforations. To place the pack in this manner, it is necessary to placea sand-retaining screen in the well bore below the upper perforations,so as to intercept gravel entering the lower perforations from thecavity 12, and then connect the upper perforations to the tubing outlet.That is, apparatus may be used which will enable the gravel pack to beplaced as the slurry is circulated vertically through the cavity 12,with `at least some of the ltrate returning to the well rather thanpassing into the formation.

Our invention therefore should not be considered as limited to theembodiments described in detail, but its scope is properly to beascertained from the appended claims.

We claim: 1. A method of gravel-packing a washed-out section in anunconsolidated formation penetrated by a well casing having perforationsopening into said washed-out section comprising:

placing a liner in said casing to seal said perforations, makingmultiple upper or lower perforations through said casing and liner nearthe upper and lower extremities respectively of said washed-out section,

lowering a uid conduit in said well, said conduit having agravel-retaining screen attached to the lower end thereof with a checkvalve in said screen in cornmunication with said uid conduit, saidscreen having near each of its top and bottom ends an annular uid sealbetween it and said liner and a soluble material sealing its openingsexcept near said bottom end,

positioning said screen opposite said upper perforations and above saidlower perforations, with said topend Seal @Qing 'lbQVtall@ saidbottom-end seal being below said upper perforations,

circulating a slurry of gravel in a carrier liquid through said conduitand check valve and thence through said lower perforations into saidwashed-out section, while at least a part of said carrier liquid returnsto said well through said upper perforations and screen, therebydepositing said gravel in said washed-out section and against saidscreen,

disconnecting said flow conduit from said screen and depositing asolvent for said soluble sealing material in said screen, and

thereafter removing said solvent and dissolved sealing material fromsaid screen.

2. A method of gravel-packing a washed-out section in an unconsolidatedformation penetrated by a well casing having perforations opening intosaid washed-out section comprising:

placing a liner in said casing to seal said perforations,

perforating said casing and liner with upper and lower perforationsrespectively; near the upper and lower extremities of said washed-outsection,

placing a screen in said liner opposite said upper perforations, theupper portion of said screen being sealed with a temporary pluggingmaterial, said screen having means respectively above and below saidupper perforations for effecting a fluid seal between said liner andeach of the ends of said screen,

injecting a slurry of gravel in a carrier liquid into said well belowsaid screen, whereby said slurry enters said lower perforations and atleast part of said carrier liquid returns to said well through saidupper perforations, while depositing gravel in said washedout section,

continuing to inject said slurry and remove carrier liquid until saidgravel lls said washed-out section, and

thereafter removing said temporary plugging material from the upperportion of said screen. 3. A method of gravel-packing a washed-outsection in an unconsolidated formation penetrated by a well casinghaving perforations opening into said washed-out section comprising:

placing a liner in said casing to seal said perforations, makingmultiple upper and lower perforations through said casing and liner nearthe upper and lower eX- tremities, respectively, of said washed-outsection,

placing in said liner at least opposite said upper perforations agravel-retaining screen having a check valve in its lower end, a Huidseal between the body of said check valve and said liner above saidlower perforations, and a uid seal between said screen and said linerabove said upper perforations,

circulating a slurry of gravel in a carrier liquid through said checkvalve and said lower perforation into saidV washed-out section, with atleast part of said carrier liquid returning to said casing through saidupper perforations and screen after depositing said gravel in saidwashed-out section, until said section is substantially completelygravel-filled, and

removing the excess of said gravel from said well casing.

4. The method of claim 3 wherein said gravel comprises angular particlesat least weight percent of which pass a lO-mesh and are retained on a60-mesh U.S. Standard sieve screen.

References Cited by the Examiner UNITED STATES PATENTS 2,207,334 7/40Reynolds et al. 166--19 2,224,630 12/40 Dean et al. 166-51 X 2,844,2057/58 Carothers 166--35 X CHARLES E. OCONNELL, Primary Examiner.

3. A METHOD OF GRAVEL-PACKING A WASHED-OUT SECTION IN AN UNCONSOLIDATEDFORMATION PENETRATED BY A WELL CASING HAVING PERFORATIONS OPENING INTOSAID WASHED-OUT SECTION COMPRISING: PLACING A LINER IN SAID CASING TOSEAL SAID PERFORATIONS, MAKING MULTIPLE UPPER AND LOWER PERFORATIONSTHROUGH SAID CASING SAID LINER NEAR THE UPPER AND LOWER EXTREMITIES,RESPECTIVELY, OF SAID WASHED-OUT SECTION, PLACING IN SAID LINER AT LEASTOPPOSITE SAID UPPER PERFORATIONS A GRAVEL-RETAINING SCREEN HAVING ACHECK VALVE IN ITS LOWER END, A FLUID SEAL BETWEEN THE BODY OF SAIDCHECK VALVE AND SAID LINER ABOVE SAID LOWER PERFORATIONS, AND A FLUIDSEAL BETWEEN SAID SCREEN AND SAID LINER ABOVE SAID UPPER PERFORATIONS,CIRCULATING A SLURRY OF GRAVEL IN A CARRIER LIQUID THROUGH SAID CHECKVALVE AND SAID LOWER PERFORATION INTO SAID WASHED-OUT SECTION, WITH ATLEAST PART OF SAID CARRIER LIQUID RETURNING TO SAID CASING THROUGH SAIDUPPER PERFORATIONS AND SCREEN AFTER DEPOSITING SAID GRAVEL IN SAIDWASHED-OUT SECTION, UNTIL SAID SECTION IS SUBSTANTIALLY COMPLETELYGRAVEL-FILLED, AND REMOVING THE EXCESS OF SAID GRAVEL FROM SAID WELLCASING.